Lubricating oil compositions



'provide lubricating oil compositions United States Patent O 2,795,550 LUBRICATING OIL COMPOSITIONS Oliver L."Harle, Berkeley, John R. Thomas, Albany, and Andrew D. Abbott, Ross, Calif., assignors to California 'Research Corporation, San Francisco, Calif., is corporation of Delaware No Drawing. Application June 29, 1954, Serial No. 440,262 3 Claims. (Cl. 252-495) This invention relates to novel lubricant compositions. More particularly, the invention is concerned with novel lubricating oil compositions having improved oxidation and corrosion inhibiting properties.

Lubricating oils generally have a tendency to deteriorate due to oxidation and form decomposition products which are corrosive to metals. Since lubricating oils in use today almost invariably come into contact with metal surfaces, the problem of overcoming oxidation and corrosion is considered to be one of major importance. Opcrating conditions encountered in modern internal combustion engines in which these oils are commonly employed involve increased temperatures, higher speeds and reduced clearances which tend to promote decomposition and the formation of corrosive products. Furthermore, these engines generally employ alloy metal bearings which, besides their possible catalytic effect on the decomposition of the hydrocarbon type mineral lubricating oils, are easily corroded and this, in turn, has seriously accentuated the oxidation and corrosion problems in-rnineral lubrieating oils.

Inhibitors have been added to lubricating oils to improve their resistance to decomposition and avoid corrosivity. Mineral lubricating oils for internal combustion engines, due to the severity of their service, have also been compounded with additional agents such as wear inhibitors, sludge inhibitors and detergents to loosen and suspend products of decomposition and counteract their effect. Unfortunately, many of these agents may adversely affect the efiiciency of the oxidation and corrosion inhibitors and it is a problem to find inhibitors which will function in combination with them. Furthermore, some of the most effective oxidation and corrosion inhibitors contain active sulfur and are, therefore, extremely corrosive to silver and similar metals which are subject to attack by active sulfur. These types of metals, although once not so widely used in contact with lubricating oils and therefore considered to constitute only a minor prob- 1 lem, are being increasingly employed today. Particularly in certainimporta'nt classes of internal combustion engines as, for example, marine and railroad diesel engines, silver metal-containing bearings are more and more com- "mon and the problem of providing proper lubrication for them is one of major importance.

It is, therefore, a general object of this invention to having improved antioxidant and anticorrosion properties.

A more particular object of the invention is to provide lubricating oil compositions which are noncorrosive to silver and similar metals.

Anothermore particular object is the provision of mineral lubricating oil compositions in which the tendency to corrode alloy bearings of internal combustion engines has been inhibited.

A further and somewhat related object is to provide compounded mineral lubricating oil compositions having improved anticorrosion properties without adversely affect-ing the stabilizing, deterging and lubricating qualities of'the' hydrocarbon oil composition.

Another and still more particular object of the invention is the provision of mineral lubricating oil compositions which are noncorrosive to silver metal-containing bearings of the type employed in railroad diesel engines.

Patented June 11, 1957 "ice Additional objects of the invention will become apparent from the description and claims which follow.

in the accomplishment of the above objects, it has been found that compositions comprising an oil of lubricating viscosity and a complex of a metal compound selected from the group consisting of acids, oxides and salts of molybdenum with a metal chelating agent having two functional groups, not more than one of which is a hydroxyl radical, in vicinal or beta position to one another on the carbon skeleton of a hydrocarbon linkage have greatly enhanced anticorrosion properties. It has also been found that, in particular, compositions comprising a compounded mineral lubricating oil for internal combustion engines which is normally corrosive to alloy bearings and such chelates are substantially noncorrosive.

The metal chelating agent referred to above is the accepted terminology for a definite and well-known class of chemical compounds. Such compounds have been heretofore described in many published texts including the recent book entitled Chemistry of the Metal Cbelate Compounds by Martel] and Calvin which was published by Prentice-Hall, Inc. of New York in 1952. For present purposes the more suitable compounds of this class are members of the group consisting of dithiols, diamines, mercapto alcohols, amino alcohols. amino thiols, dicarboxylic acids, hydroxycarboxylic acids, mercoptocarboxylic acids, aminocarboxylic acids, beta-diketones, betaketo carboxylic acid esters, dimercapto benzenes, mercaptohydroxy benzenes, diamino benzenes, aminohydroxy benzenes, aminomercapto benzenes, hydroxycarboxy benzenes, aminocarboxy benzenes, and mcrcaptocarboxy ben- Zenes having the two functional groups in vicinal or beta position to one another on the carbon skeleton.

The normal tendency of oils to become oxidized and corrosive is definitely inhibited in the improved compositions of the invention. Metal surfaces in general are not corroded by contact with these compositions and internal combustion engine alloy bearings, in particular, are re markably benefited. Bearings of silver and similar metals which, as stated above are increasingly important due to their presently expanded use in marine and railroad diesel engines, are not corroded by these compositions whereas conventional oxidation inhibited oils have severely pitted and corroded such bearings. The advantages of these improvements are obtained in the compositions of this invention without loss of stability or detergency in the composition.

The complexes of the lubricating oil compositions according to this invention are prepared by the reaction of a mixture of the acid, oxide or salt of the metal and chelating agent. The mixtures are ordinarily heated to accelerate the reaction. Although the nature of the reactionis not definitely known, it is believed that two of the functional groups of a single hydroxycarboxylic acid, dithiol, dicarboxylic acid, etc. react with the acid to form what is commonly termed a metal chelate compound. These compounds are characterized by a "claw" type of structure in which one or more rings of similar or unlike structure due to the use of mixed chelating agents are formed including the molybdenum.

The preferred chelates of the above type are oil-soluble and the chelating agents are usually selected so as to impart oil solubility to the complex or chelate. Chelating agents containing from 2 to 18 carbon atoms are usually suitable since the less oil-soluble chelates may be used in combination with dispersants such as alkaline earth metal petroleum sulfonatesor oil-solubilizing agents such as glycols and other polyhydric alcohols as-well as ethers thereof. Those containing from 6 to 10 carbon atoms in the carbon skeleton are preferred since they impart an optimum degree of oil solubility to the chelate or complex.

Examples of suitable chelating agents within the above-described class include vicinaland beta-dithiols such as ethylene mercaptan and 1,3-propanedithiol; vicinaland beta-mercapto alcohols such as beta-mercaptoethanol, 3 mercapto-l-propanol; vicinaland beta-diamines such as ethylenediamine and propylenediamine; vicinaland beta-amino alcohols such as ethanolamine and 3-amino-l-propanol; vicinaland beta-aminothiols such as thioethanolamine and 3-amine-l-mercaptopropane; vicinaland beta-dicarboxylic acids such as oxalic acid and malonic acid; vicinaland beta-hydroxy carboxylic acids such as glycolic acid and beta-hydroxybutyric acid; vicinaland beta-mercapto carboxylic acids such as thioglycolic acid and beta-mercaptobutyric acid; vicinaland beta-amino carboxylic acids such as glycine and beta-aminobutyric acid; beta-diketones such as acetylacetone and benzoylacetone; beta-ketocarboxylic acid esters such as ethyl acetoacetate; etc. The foregoing compounds are characterized by normal or branched carbon skeletons. in various positions along the carbon skeleton, aromatic and substituted aromatic rings; hydroxy, alkoxy, and aryloxy radicals; sulfhydryl, alkylthioether, arylthioether, alkylthioester, and arylthioester groups; acyl, aroyl, thioacyl and thioaroyl radicals; amino, alkylamine, arylamino, acylamido and aroylamido radicals; and nitro, halogen and sulfato groups. However, preferred chelating agents of the aforementioned type for present purposes are those having an aliphatic hydrocarbon group between the two functional groups.

Also suitable as chelating agents are various carbocyclic or aromatic chelating agents including vicinal-dimercaptoaromatic compounds such as thiocatechol; vicinal-mercaptohydroxy aromatic compounds such as monothiocatechol or mercaptohydroxy benzene; vicinaldiaminoaromatic compounds such as o-phenylenediamine; vicinal-aminohydroxyaromatic compounds such as o-aminophenol; vicinal-aminomercaptoaromatic compounds such as o-aminothiophenol; vicinal-hydroxycarboxyaromatic compounds such as salicylic acid; vicinalaminocarboxyaromatic compounds such as o-aminobenzoic acid; vicinal-mercaptocarboxyaromatic compounds such as omercaptobenzoic acid; etc. The aforementioned carbocyclic or aromatic chelating agents may have various ring substituents including aromatic and substituted aromatic rings; hydroxy, alkoxy, and aryloxy radicals; sulfhydryl, alkylthioether, arylthioether, alkylthioester, and arylthioester groups; acyl, aroyl, thioacyl and thioaroyl radicals; amino, alkylamino, arylamino, acylamido, and aroylamido radicals; and nitro, halogen and sulfate groups. For present purposes those aromatic chelating agents having the two functional groups on a benzene ring or an alkyl benzene containing from 2 to 18 carbon atoms in the alkyl group are preferred since the chelates of the above-described metals prepared with them possess the most satisfactory oil-solubility characteristics.

For present purposes the chelating agents most preferred out of the above-described classes are the aliphatic and carbocyclic vicinaland beta-dicarboxylic and hydroxycarboxylic acids of from 2 to 18 and preferably 2 to 10 aliphatic carbon atoms. Illustrative chelating agents of this particular group are alpha-hydroxyacetic acid (glycolic acid), alpha-hydroxydecanoic acid, betahydroxystearic acid, salicylic acid, cetylsalicylic acid, 2- hydroxy-cyclohcxanoic acid, tetrahydrophthalic acid, tartaric acid, citric acid, lactic acid, glutaric acid, oxalic acid, malonic acid, phthalic acid, etc. These chelating agents give complexes of the previously described types which are superior corrosion and/or oxidation inhibitors in the lubricating oil compositions of the invention.

Although it is convenient for the sake of illustration in the above description of the invention to refer to the reaction of an acid of molybdenum with the various chelating agents or mixtures thereof to form the com- They may have substituted plexes for the lubricating oil compositions, other compounds of molybdenum such as the oxides and salts mentioned above may also be employed to provide similar chelates. Suitable acids include molybdic acid or molybdic hydroxide and molybdic anhydride as illustrative examples. Oxides of molybdenum which form complexes with the chelating agents adapted for use in the lubricating oil compositions of the invention are illustrated by compounds such as molybdenum sesquioxide, etc. Suitable salts are the inorganic salts such as ammonium paramolybdate, ammonium molybdate, molybdanyl chloride, etc.

Various amine salts of the acid complexes of molybdenum and chelating agents referred to above may also be employed advantageously in the lubricating oil compositions of the invention. These amine salts are conveniently prepared by heating a mixture of the acid complex with an organic amine such as trimethylamine, triethanolamine, laurylamine, phenyl-alpha-naphthylamine, phenylene diamines, aminophenol, pyridine, and morpholine. Esters of the acid complexes such as the monobutyl esters and monopentaerythritol esters are also suitable. Such substituted complexes are generally characterized by enhanced oil solubility which may be desirable in the compounding of certain mineral lubricating oil compositions.

The complex of molybdenum described above is present in the compositions of the invention in an amount at least suflicient to inhibit corrosion or oxidation. Small amounts, usually from about 0.01 to about 5.0 percent by weight based on the oil, are etfective. Proportions ranging from about 0.05 to about 1.0 percent are preferred in most lubricating oil compositions. Concentrates containing larger proportions, up to 50 percent, either in solution or suspension, are particularly suitable in compounding operations.

Any of the well-known types of oils of lubricating viscosity are suitable base oils for the compositions of the invention. They include hydrocarbon or mineral lubricating oils of naphthenic, paratfinic, and mixed naphthenic and paraflinic types. They may be refined by any of the conventional methods such as solvent refining and acid refining. Synthetic hydrocarbon oils of the alkylene polymer type or those derived from coal and shale may also be employed. Alkylene oxide polymers and their derivatives such as the propylene oxide polymers and their ethyl esters and acetyl derivatives in which the terminal hydroxyl groups have been modified are also suitable. Synthetic oils of the dicarboxylic acid ester type including dibutyl adipate, di-2-ethylhexyl sebacate, di-nhexyl fumaric polymer, dilauryl azelate, and the like may be used. Alkyl benzene types of synthetic oils such as tetradecyl benzene, etc. are also included. Liquid esters of acids of phosphorus including tricresyl phosphate, diethyl esters of decane phosphonic acid, and the like may also be employed. Also suitable are the polysiloxane oils of the type of polyalkyl, polyaryl, polyalkoxy and polyaryloxy siloxanes such as polymethyl siloxane, polymethylphenyl siloxane and polymethoxyphenoxy siloxane and silicate ester oils such as tetraalkyl and tetraaryl silicates of the tetra-Z-ethylhexyl silicate and tetra-p-tert.-butylphenyl silicate types.

In a preferred embodiment of the invention, as mentioned above, the complexes are employed in combination with compounded mineral lubricating oils of the internal combustion engine type which are normally corrosive to alloy bearings. In such an embodiment, as in the case of the other, straight oils of lubricating viscosity, at major proportion of the lubricating oil normally corrosive to metals and/or subject to oxidation and a small amount, sufficient to inhibit said corrosion and/or oxidation, of the complex provides a remarkably improved composition. These compounded oils customarily contain detergents such as the oil-soluble petroleum sulfonates and stabilizers such as the metal alkyl phenates. Other EXAMPLE 1 To a solution prepared from 36 grams (0.25 mole) of molybdenum trioxide and 150 milliliters of concentrated ammonium hydroxide (28% ammonia) in a 2-liter, 3- necked flask is added 200 milliliters of toluene and 63 grams (0.50 mole) of oxalic acid dihydrate. The mixture is refluxed with continuous water separation. A deep blue color appears after about 15 minutes. After complete removal of the water, the mixture is heated for one hour at 250 F. The toluene is then removed by distillation and 300 grams of ethylene glycol is added. After stirring for one-half hour at 250 F., 500 grams of basic calcium petroleum sulfonate in neutral mineral lubricating oil analyzing 4.35% calcium is added and the ethylene glycol removed by distillation at 385 F. under 50 mm. Hg pressure. The resulting solution of oxalic acid molybdate is used as a concentrate in blending test oils. By analysis, the per cent molybdenum is 3.25.

EXAMPLE 2 A slurry of 50 parts of ammonium paramolybdate and 60 parts of a 70% aqueous solution of glycolic acid in 100 parts of toluene is heated with stirring at reflux tem perature and the azeotropic water is separated and removed. A deep blue-green color appears after about 15 minutes. The reaction is complete after about 45 minutes. 500 parts of a basic calcium petroleum sulfonate concentrate in neutral mineral lubricating oil analyzing 4.35% calcium is added and the mixture is stirred and heated at 380 F. under 50 mm. Hg pressure for 30 minutes to remove the last traces of water. The product consisting of neutral mineral oil, glycolic acid molybdate and calcium petroleum sulfonate is filtered and used as a concentrate. Analysis of the concentrate shows about 2.3% molybdenum.

The effectiveness of the lubricating oil compositions of the invention is demonstrated by the copper-lead strip corrosion test. In this test a polished copper-lead strip is weighed and immersed in 300 cubic centimeters of test oil in a 100-milliliter lipless Berezelius breaker. The test oil is maintained at 340 F. under a pressure of one atmosphere of air and stirred with a mechanical stirrer at 1000 R. P. M. After two hours a synthetic naphthenate catalyst is added, unless otherwise specified, to provide the following catalytic metals:

Percent by weight Iron 0.008 Lead 0.004 Copper 0.002 Manganese 0.005 Chromium 0.004

The test is continued 20 hours. The copper-lead strip is then removed, rubbed vigorously with a soft cloth and weighed to determine the net weight loss.

The test oils include various types of mineral lubricating oil compositions as reference oils. compounded oil (A) consists of a solvent refined SAE 40 mineral lubricating oil base having a viscosity index of 60 and containing 40 millimoles per kilogram of neutral calcium petroleum sulfonate. compounded oil (B) consists of the same base oil but contains 20 millimoles per kilogram of basic calcium petroluem sulfonate. Th test results are shown in the following table. The concentrations of complex employed are given in millimoles of molybdenum per kilogram of oil or percent by weight of the composition.

Table I COPPERLEAD STRIP CORROSION TEST Copper- Oil Lead Strip Weight Loss e -J Reference oil (A) 225.0 20 mMJkg. glycolic acid molybdate in reference oil (A)... 1.0 20 mM./kg. oxalic acid molybdate in reference oil (A) 10. 7 Reference oil (B) 219. 0 10 mMJkg. glycolic acid molybdate in reference oil (B). 3. B

As shown by the above test data, the reference mineral lubricating oil compositions alone give copper-lead strip weight losses due to corrosion of as high as 225 milligrams in the 20hour period. By way of distinction, compositions in accordance with this invention containing the same mineral lubricating oil base and a complex of the previously described type give as little as 1.9 milligrams for the same period. This shows that the compositions of the present invention are effectively inhibited against oxidation and/or corrosion characteristics due to the oxidative deterioration of the oil.

The nature of the improved lubricating oil compositions of the invention and their effectiveness should be readily apparent from the many illustrations given above. Oxidation and corrosivity in the compositions are definitely inhibited to a very substantial degree. Particularly corrodible metals such as engine alloy bearings of copper, lead, and the like, as well as bearings of silver, are not adversely affected. This is indeed remarkable since the problem of devising lubricant compositions uniformly noncorrosive to both types of bearing metals has long confronted workers in the art. The advantages of these improvements are obtained without loss of other desirable properties of the lubricant compositions.

Although the compositions of the invention have been primarily described as crankcase lubricants for internal combustion engines, they are also useful as turbine oils, hydraulic fluids, instrument oils, constituent oils in grease manufacture, ice-machine oils, and the like.

We claim:

1. A lubricant composition consisting essentially of a mineral lubricating oil for internal combustion engines containing minor amounts of alkaline earth metal petroleum sulfonate and alkaline earth metal alkyl phenate, which is normally corrosive to alloy bearings, and from 0.01 to about 5.0 percent by weight based on the oil of a member of the group consisting of glycolic acid molybdate and oxalic acid molybdate.

2. A lubricant composition consisting essentially of mineral lubricating oil for internal combustion engines containing minor amounts of alkaline earth metal petroleum sulfonate and alkaline earth metal alkyl phenate which is normally corrosive to alloy bearings and from about 0.01 to about 5.0 percent by weight based on the oil of glycolic acid molybdate.

3. A lubricant composition consisting essentially of mineral lubricating oil for internal combustion engines containing minor amounts of alkaline earth metal petroleum sulfonate and alkaline earth metal alkyl phenate which is normally corrosive to alloy bearings and from about 0.01 to about 5.0 percent by weight based on the oil of oxalic acid molybdate.

References Cited in the file of this patent UNITED STATES PATENTS 2,144,654 Guthmann Ian. 24, 1939 2,161,184 McKone et al. June 6, 1939 2,305,627 Lincoln et al. Dec. 22, 1942 2,465,296 Swiss Mar. 22, 1949 

1. A LUBRICANT COMPOSITION CONSISTING ESSENTIALLY OF A MINERAL LUBRICATING OIL FOR INTERNAL COMBUSTION ENGINES CONTAINING A MINOR AMOUNTS OF ALKALINE EARTH METAL PETROLEUM SULFONATE AND ALKALINE EARHT METAL ALKYL PHENSATE, WHICH IS NORMALLY CORROSIVE TO ALLOY BEARINGS, AND FROM 0.01 TO ABOUT 5.0 PERCENT BY WEIGHT BASED ON THE OIL OF A MEMBER OF THE GROUP CONSISTING OF GLYCOLIC ACID MOLYBDATE AND OXALIC ACID MOLYBDATE. 